Recently, to reduce pollution from fossil fuel power plants much effort has focused on developing both processes and hardware for zero emission power plants. A key component of these efforts includes improving synthesis gas generators, or reactors, which produce hydrogen fuel from low value carbonaceous feedstock such as coal and petcoke. In typical synthesis gas reactors coal, oxygen, and water react to produce the high energy content synthesis gas (hydrogen and carbon monoxide). In the meantime, water flows through a reactor coolant liner to protect the reactor walls from excessive temperatures. In turn, the resulting heated water is fed back into the reactor as the water reactant, thereby regeneratively cooling the reactor.
Prior art coolant liners for synthesis gas reactors are expensive to build and often suffer from low reliability. For instance, some coolant liners use unprotected metal tubes to contain the water coolant as it warms and boils at temperatures below 700 degrees Fahrenheit. Because the gasification occurs near 3000 degrees Fahrenheit, the hot-side metal wall surface temperatures can easily approach 1200 degrees Fahrenheit. These surface temperatures can prove fatal for any long life metal component operating in the alkali slag and sulfur laden product gases in the reactor.
Other prior art reactor coolant liners use thin layers of ceramic coatings (alumina, chromia, or silicon carbide) deposited on the metal tubes to freeze a protective slag layer on top of the thin ceramic coating. However, the protective layer constantly spalls due to thermal shocks and coefficient of thermal expansion mismatches between the protective slag, the ceramic, and the metal tube. Thus, where the protective slag and ceramic coating spalls, the alkali and sulfur compounds attack, and eventually damage, the metal tube. Because of these problems, the prior art reactors suffer from a low mean time between failure, often on the order of mere months.
Other syntheses gas reactors avoid these problems by employing monolithic ceramic brick liners to protect the reactor from damage induced by the high temperatures and corrosive gases. Unfortunately, these monolithic liners require replacement about annually. Since the monolithic liners include high chromia content for resistance to corrosion from the alkali and sulfur laden gases, each replacement can represent a very substantial cost. Moreover, whether a monolithic ceramic or a ceramic coating is employed, these prior art reactors require approximately 12 hours or more to safely warm up and cool down to avoid thermally shocking, and damaging, the ceramics. Accordingly, the requirement for gradual transients hinders the operation of synthesis gas plants, and critically so during emergencies.
Thus a need exists to improve regeneratively cooled synthesis gas reactors.